Aggressive new cat - rehome?

[MrTiddlesTheCat]

What do I do? A little stray moved himself into my house in August. He's a tiny thing and so friendly to humans, but he's being mean to my other cats. Not all the time, but enough to see they are scared of him. At first they were fine but the last couple of weeks have upset me. Maybe because it's suddenly got colder here so they're all in more.

Do I ignore it and hope it settles down as they learn to coexist? I've tried feliway but it made everyone sick. Will it get better or does he need to go? Or is it normal behaviour in cat families? It's full on screeching at each other 2 or 3 times a week.

My poor big boy is terrified. He's a 6 year old male 3x the size of the scrapper, but he's as soft as butter. My female isn't so scared as she's a scrapper herself with anger issues, but she's an old lady now.

I'm so sad.

Gin.
What you're describing to me sounds like fairly normal multi cat household behaviour.
I have 4 cats, although no 4 doesn't come in the house, so the in-house dynamics are 3 way.
The two who get on best also are the two who scrap with each other. They're sisters. They are either sleeping together, hanging out together or chasing each other and scrapping. It can sound like they're murdering each other but it's all noise and they never actually hurt each other.
All three eat in the same room and sleep in the same room during the day (it's the warmest room) so despite them not being besties I think they accept each other.